1. Field of the Invention
This invention relates to helicopter controls, and more particularly to controls enabling flying of a helicopter to maximum loading within its structural envelope.
2. Description of the Prior Art
As is known, the loads in the rotor system of a helicopter may vary widely as a function of airspeed; at certain airspeeds, slight vertical maneuvering can cause vast changes in rotor load. This is particularly true at high airspeeds, wherein the retracting blade travels at such a low rate of speed that it has relatively small lift, which results in excessive loading of one side of the rotor, which in turn causes vibration that can become severe, and alternately results in blade stall. In the older and simpler helicopters, vibration feeds back through the control system to the collective pitch control stick, such that the pilot, by sensing the vibration, can fly the aircraft at high performance, without exceeding safe loads. In large and sophisticated helicopters, the utilization of control systems which isolate the rotor from the sticks which control it together with design improvements which reduce the amount of vibration as a function of loading, have resulted in loss of the vibration-indication of rotor blade loading. As a substitute it is known to measure the force required for the main rotor actuating mechanism to move the swashplate (which alters the pitch of the blades) by means of an electromechanical transducer, which provides an indication of rotor loading on a cockpit panel instrument, called a cruise guide indicator. However, load measurement devices have been found to be extremely inaccurate and unreliable; and, concentration on a load indicator detracts from the maneuvering in which the pilot is involved. Additionally, the amount of loading varies as a function of a number of variables within the extremes of the structural envelope. Therefore, maneuvering the aircraft to any particular load as indicated by a force or load measuring device could not permit maximum maneuvering of the aircraft within the structural envelope.